1. Field of the Invention
The present invention relates to means for providing ions in a fluid and more particularly to means for producing a substantially uniform source of ions having an electric charge of the same sign.
2. Description of the Prior Art
Ions have been found to be very useful in sensing various parameters such as the flux, velocity, or mass flow of a fluid. A typical example of one such application is described in the patent to G. L. Mellen, U.S. Pat. No. 2,637,208 entitled Velocity Measuring By The Use Of High Energy Electrons. Mellen teaches the formation of an ion cloud at a known location and detecting the arrival of such ions at a second location. Means such as a spark gap or ionizing radiation provide the ion cloud required for the measurement. A generally similar teaching is provided by B. Boyd et al in U.S. Pat. No. 2,827,786 entitled Ion Tracer Airspeed Indicator. Boyd et al time the passage of an ion cloud between two known locations and disclose several possible methods of producing the required ionization such as alpha particles, high speed electrons, ultraviolet rays, x-rays and the spectrum of available electric discharges although the art does not dwell on the relative merits of each of such sources.
In U.S. Pat. No. 3,470,741 entitled Mass Flow Meter Apparatus, E. J. Durbin describes a mass flow apparatus having a line source ionization means which is either linear or in the form of a circular disc. Durbin discloses a corona discharge as the means for providing ions although other ion sources are suggested and equally applicable. One of the principal shortcomings of the ionization producing means shown is the sensitivity to particulate matter passing through the device. Foreign particulate matter such as dust or dirt which may be entrained in the fluid entering the system can settle on the emitting electrode causing a nonuniformity in the distribution of emission from the electrode. Similarly, foreign material suspended in the fluid stream itself especially in the areas directly adjacent to the emitting electrode can lead to erratic ion current behavior due to perturbations in the charge distribution in this region. A power supply including means for maintaining a constant ratio of voltage to current between the emitting and collecting electrodes of ion deflection devices is taught in U.S. Pat. No. 3,648,517 entitled Control Apparatus For Mass Flow Meter issued to F. D. Dorman. Although the control for the power supply as disclosed has certain advantages, the basic mass flow meter apparatus disclosed is essentially the same as devices shown in the prior art. A simple and reliable source of ions which is insensitive to the presence of such foreign matter would enhance the practicableness of many devices such as the instruments briefly discussed above.